1. Field of the Invention
This invention relates to picture display apparatus utilized with a display device such as a liquid crystal device (LCD) in which picture cells (pixels) are arranged in a mosaic pattern.
2. Background
In an picture display apparatus utilized with a display device such as a LCD in which pixels are arranged in a mosaic pattern, it is required to increase a number of pixels to increase resolving power of the apparatus. However, because the production yield of acceptable product is decreased, it is impossible to increase the number of pixels without limitation and make the space between pixels smaller.
When a large screen is made of this kind of picture display apparatus, a viewer may recognize dots of pixels or a grid based on the space between pixels (for example, a portion having black stripes in LCD). In an color picture display apparatus of this kind, color filters for the primary three colors or the corresponding three different colors are disposed in front of the pixels at a certain repeated frequency. However, when the screen becomes large, the frequency of pixel dots disposed with the same color filters can be easily recognized and therefore, lowers image quality.
For a charged coupled device (CCD) camera, it can become difficult to recognize the space between pixels by electronic processes such as low pass filters. But, the electronic process may not be available for making the pixel dots and the grid unrecognizable in the picture display apparatus such as the LCD display apparatus, because it is necessary to make up the space between pixels after a light is generated. As a compromise, there is a method to unfocus the viewer's lens focus. However, it does not result in the preferable condition, because the signal is also unfocussed.
A technique to render it difficult to recognize the grid between pixels has been developed, as described for example in a Japanese laid-open patent application Sho 59-214825. In the apparatus, a diffraction grating is placed in front of the display device such as a LCD. A light from a pixel is diffracted into a plurality of lights so that an image of a pixel can be focussed on a viewer's retina as a plurality of virtual images out of a plurality of pixels. The diffusion of pixel is so performed that the focussed position of diffracted image can be located on the grid position between the pixels. As the result, the grid between the pixels can become difficult to recognize.
FIG. 13 shows an example of the conventional picture display apparatus. An LCD 1 has a plurality of pixels placed along directions of height (column) and width (row). A back light member 2 is provided to provide a light from behind and make the display at the LCD 1 bright. An ocular lens 4 is disposed in front of the eyes of a viewer 5. A diffuser 3 (optical filter) is placed between the LCD 1 and the ocular lens 4. The diffuser 3 is formed by a transparent plate which has a diffraction grating 3A on its surface working as an optical filter surface for image diffusion.
FIG. 14 is a drawing to explain the dispersion of light out of a pixel through the diffraction grating. In this drawing, a pixel 11 shows, for example, one of a plurality of pixels in the LCD 1. A diffraction grating 3A works as an optical filter surface. The diffraction grating 3A is disposed at a position P2 which has a distance d away from a position P1 where the pixel 11 is located on the surface of the LCD.
As shown in FIG. 14, light from the pixel 11 is diffracted by the diffraction grating 3A. As an image of the pixel 11, the viewer of this apparatus can see a zero order image which goes straight through the diffraction grating 3A, and virtual images of 1st and 2nd orders at positions each shifted by a distance X which is determined by a pitch g of the diffraction grating 3A and the distance d. By designing to make these virtual images of 1st and 2nd orders overlap at the outlined portions between pixels, it becomes difficult to recognize the dots of the pixels and the grid between the pixels.
However, there has been some problem as described below in the conventional picture display apparatus because the optical filter surface for the picture diffusion is formed as a single surface.
In the conventional technique, it has been difficult to control the diffusion for more than three (3) pixels. In other words, with the diffraction grating 3A, it is difficult to control the luminance level of the diffracted light in the higher order. Also, a total number of images of the diffused pixels can not be easily increased because of the diffusion by a single optical filter surface. The directions obtained by the diffusion with a single optical filter surface have also been limited up to two (2) axes which are perpendicular to each other. Since there is no flexibility to design the apparatus due to the above reasons, the most appropriate image cannot be obtained by the pixel diffusion.